Specialty beverages in which at least a portion is made up of frothed or heated milk are becoming more and more popular. The best-known beverage of this type is a coffee of the cappuccino type. It comprises a liquid portion consisting of coffee topped by a layer of frothed milk which, because of its very much lower density, floats atop the surface of the liquid. In general, preparing one takes time, manipulation operations and cleaning.
The most customary way of preparing a milk-based froth is to pour the desired amount of milk into the container, immerse a steam outlet pipe from a coffee machine in the container, agitating it up and down to introduce the air needed to form the froth.
There also exists mechanical stirring appliances which are usually intended for domestic use for beating froth from more or less viscous food products such as eggs, ice, juices or the like. The problem with these appliances is of several natures which means that they are ill-suited to producing froth from a milk-based liquid for making a beverage. One disadvantage, for example, stems from the fact that these appliances stir a liquid or a paste in the cold state, considerably limiting their potential use. In addition, milk does not froth as convincingly when cold or at ambient temperature.
Another disadvantage stems from the fact that these appliances are ill-suited to frothing the microbiologically sensitive liquids such as milk. Regular cleaning of the tank of the appliance needs to be envisaged in order to remove any solid food residue. In addition, heating the milk has a tendency to increase the extent to which cooked or burnt proteins are deposited on and adhere to the surfaces. The existing appliances are not, for the most part, well suited to reducing the encrustation of this solid residue, making cleaning troublesome.
These appliances also have a stirring and drive mechanism which is fixed and intrudes into the tank, and this presents several disadvantages: the removal/refitting time is not insignificant, they have a tendency to become soiled more quickly, they entail additional cost as a result of the multiplicity of components, and the stirring means are difficult to clean.
Another disadvantage with these appliances stems from the fact that frothing in these appliances is not optimal for reasons associated with the arrangement of the stirring means. Some appliances have a stirring means positioned in the middle of the tank. Such an arrangement is not efficient in quickly converting a volume of milk-based liquid into a rich froth.
Other appliances have several stirrers. These arrangements are generally mechanical with gearing means needed to coordinate the rotation of the stirrers, and this makes the system intrusive, and therefore less hygienic, increases the number of parts and makes cleaning a more painstaking operation.
U.S. Pat. No. 6,318,247 relates to an appliance for preparing hot beverages or food with stirring such as hot chocolate, for example. The appliance comprises a system for driving a stirrer of the magnetic effect type. It does, however, have several disadvantages. Firstly, in such an appliance, the liquid or froth is stirred coaxially with respect to the central axis of the tank, and this causes a circulation in which some layers of liquid or froth, particularly the peripheral layers, are not stirred as extensively as others, particularly the layers near the middle, because of the centrifuging effect produced by the stirrer. Such a circulation is therefore not suited to producing a froth of sufficient quality or to reducing the time needed to produce this froth. In addition, the structure of the appliance is not hygienic for treating a milk-based liquid and cleaning is not made any easier by such a construction. Other devices for stirring food products which have more or less the same disadvantages are described in patent documents WO2004/043213 or DE 196 24 648.
Stirring systems with a magnetic engagement type are described in documents U.S. Pat. No. 2,932,493, DE 1 131 372, U.S. Pat. Nos. 4,537,332 and 6,712,497 but none of these provide solutions suited to producing a quality froth in a short time and hygienically.
Utility model DE 89 15 094 relates to a refrigerated pot for dispensing a milk-based beverage. The pot comprises refrigerating means and forced-convection means in the form of a magnetic rotor. Such a device is not suited to converting the liquid into a froth but simply keeps the liquid uniformly at the refrigeration temperature for preservation.
U.S. Pat. No. 3,356,349 discloses a stirring device that has a heated tank, magnetic drive means positioned under the tank for driving a hub located in the middle of the tank. The hub is associated with a stirring element which is offset with respect to the hub, causing the element an oscillatory movement. Such a principle of stirring may create a loss in magnetic coupling because of the high moment of inertia generated by the offset position of the stirring means with respect to the axis of rotation of the drive means. This problem increases with increasing speed. Such a stirring device can therefore work to stir certain liquids or other substances at low speed but may prove ill-suited to converting liquid into a froth at sufficiently high speed. Incidentally, the document does not mention the conversion of a liquid into a froth using this device.
More recently, an improved appliance for preparing froth from a milk-based liquid or milk has been proposed in WO2006/050900. The device has: a tank for receiving the liquid that is to be frothed, in which liquid a rotatable stirrer is positioned; a stand holding the tank; drive and control means which are in a cavity located between the inner tank and the outer stand, and which communicate with a switch and electrical connections located on the outer surface of the stand; and disturbance means to optimise circulation of the milk during frothing. This invention provides a solution to the abovementioned problems. It also recognises the hygiene issues that are raised the handling of milk, in particular heated milk that deposits against inner the walls of the tank. Hence, the device disclosed in the above publication has a tank for containing the milk which has no joining lines or connections between the tank's walls and generally no gaps that would attract the deposition of solids, such as burnt milk.
However, despite the recent hygiene-related improvements regarding the preparation of the froth, it has been found that while the apparatus is handled by users, in particular un-cautious handling of the apparatus, for example when frothed milk is removed from the tank, milk may spill and stain the stand and other external parts and raise hygiene problems. The same problems may arise due to presence of the disturbance means that induce and increase agitation in the liquid and thus splashing. This problem is particularly acute in relation with switches, electrical connections and other parts of the stand that may attract milk deposits over time and cause cleaning problems and are in addition hard to clean properly without damaging the electric appliance. One way to solve this problem, at least in part, may involve the use of an appropriate lid and dispensing arrangement configured to avoid spills on the outer part of the appliance. This would however still require special attention by the user to avoid such spills.